Growing mahogany sustainably through conservation and augmentation a biological control agent of mahogany pests of

Grace T. Lim

1&2

, Scott M. Salom

1

, Laurence G. Kirton

2

, Loke T. Kok

1

,

1

Entomology Dept, Virginia Tech,

2

Entomology Unit, Forest Research Institute Malaysia

Introduction

Mahogany is among the most valuable tropical hardwoods in the world and has been harvested to commercial extinction. Numerous reforestation efforts worldwide with mahogany species, e.g.,

Swietenia macrophylla

and

Khaya ivorensis

(Meliaceae) have been foiled by the mahogany shoot borers (

Hypsipyla

spp., Lepidoptera: Pyralidae) found throughout the tropics. Eight decades of research spanning 23 countries has yet to come up with a reliable, cost-effective and environmentally sound solution to this problem.

Hypsipyla robusta,

the Shoot Attacker

Below L-R: The adult female lays eggs on a leaf axil or new shoot that a newly emerged larva will burrow into. The larva later migrates to the terminal shoot; which dies as the pith is consumed; and the tree develops multiple leaders as a result

Oecophylla smaragdina,

the Shoot Protector!

The weaver ant,

Oecophylla smaragdina

(Hymenoptera: Formicidae), inhibits infestation of mahogany by the shoot borer,

Hypsipyla robusta

, which attacks mahoganies in Asia, Australia and the Pacific Islands.

It is an aggressive predator of arthropods, including

H.

robusta

(R).

It vigilantly patrols its host plant, which includes

K.

ivorensis

(L), building nests from young leaves.

• The ant also tends ‘trophobionts’, e.g.,mealybugs (Hemiptera), in exchange for ‘honeydew’ excreta, an important food of the ant.

• The leaf nests of this ant can be ‘harvested’ from other trees and introduced to mahogany plantations to protect them.

• Protection is needed for the first three years until an unbranched height of 8 m is achieved.

International collaborative research by Virginia Tech’s Entomology Department and the Forest Research Institute of Malaysia (FRIM) is currently focusing on conservation and augmentation as biological control approaches to enhance the performance of the weaver ant against the shoot borer.

Rationale

A weaver ant colony relocated to new host plants can be conserved and augmented in a ‘two-pronged’ approach: 1. Short term: Direct food supplementation to meet energetic needs until it is self-sufficient, i.e., has cultivated enough trophobionts.

2. Long term: Indirect food provision and additional nesting sites in a more stable and diverse mixed-plantation.

Therefore, the

objectives

of this research program were to identify: 1. Preferred foods of the ant that aid colony conservation. These foods should be cheap and practical to apply.

2. A preferred alternate host plant species of the ant that can be easily grown with mahogany as a second crop.

(a)

Weaver ant formula Choice Test

Food

Assessing Food Preference of the Ant

Methods

• Choice test (R): 6 ant colonies had nest • A choice and no-choice study used mature weaver ant colonies at FRIM

ad libitum

access to 4 foods: fish, live mealworms, liquid ‘weaver ant formula’ (with body-building protein powder) and honey solution. Food amounts taken recorded daily for 7 d.

• The no-choice test was similarly conducted, but gave only one of the 4 foods to a total of 12 colonies.

• Data analysis: Kruskal-Wallis & Friedman’s tests

Results

• The ants preferred live mealworms (Fig 1.a) but accepted fish when no choice was given (Fig 1.b).

• The ants did not consume much liquid food.

Discussion

• Established colonies may get enough honeydew from trophobionts but relocated colonies have few trophobionts and may need ‘high-carb’ supplemental foods. Thus, ‘high-carb’ weaver ant formula and ‘high-protein’ mealworms chosen for next study.

nest control string treatment

Honey Mealworms Fish

(b) Ants!

Major Studies and Results

No Choice Test -5 0 5 10 15

Weight of food taken (g)

20 -5 0 5 10 15

Weight of food taken (g)

20

Figs. 1.(a-b). The average amount of four foods taken daily by

O. smaragdina

in the choice test (left) and no-choice test.(right) (± SEM, n = 6 and n = 3 for the choice and no-choice tests, respectively)

Effect of Food Supplementation on the Ant

Methods

• 12 ant colonies relocated to new mahogany host plants at FRIM.

• Half the colonies received weaver ant formula and mealworms (L-R) for 16 weeks.

• Ant activity monitored weekly on shoots, around the foods and in nest-building.

• Data analysis: GLM ANOVA.

Results and Discussion

• Food-supplemented (

F

) colonies had greater colony sizes than the

C

• colonies receiving no food.

• For

F

colonies much weaver ant formula was consumed initially (wk 1-9) then declined while ant activity on shoots and nest-building increased.

F

colonies may have ‘weaned off’ the foods after establishing.

Surveys for Host Plants of the Ant

Methods

• Four Malaysian habitats, including mangroves (R), were surveyed for host plants of the ant.

• All vegetation within 3 m of trail borders along a 1 km line transect was examined for weaver ant nests .

Results

• Four host plant species were particularly ant-abundant:

citrifolia

(Rubiaceae),

Talipariti tiliaceum

(Malvaceae),

Morinda Bruguiera

spp.

(Rhizophoraceae),

Acacia auriculiformis

(Fabaceae).

Screening Host Plant Candidates

Methods

• Three favored host plant species from the previous study were tested:

M.

citrifolia, T. tiliaceum

and

Bruguiera

spp, plus non-host

Avicennia officinalis

(Acanthaceae) as the control.

• Ant preference was evaluated using a ‘relative ant abundance index’, based on ratio of volume of nests : plant crown surface area.

• Data analysis: Kruskal-Wallis test.

Results and Discussion

• The ant was most abundant on

citrifolia

, followed by

T. tiliaceum M.

and

Bruguiera

spp. (Fig 2. below).

• Many ants aggregated on

M. citrifolia

fruit, imbibing nectar (R). Trophobionts tended by the ant on

M. citrifolia

posed no pest risk.

•

M. citrifolia

was selected for next study.

4 3

Relative ant abundance rank

2 1 (Kruskal-Wallis z value) 0 -1 -2 -3

Morinda Talipariti Bruguiera citrifolia

(9.3 ± 4.7)

tiliaceum

(1.1 ± 0.5)

officinalis

(1.3 ± 0.7) (0)

Plant species

(Relative nest volume ± SEM, cm 3 m -3 , n = 4) Fig. 2. Relative ant abundance in relation to three host plant species and one non-host plant species of

O. smaragdina

.

Future Work

A study is in progress to evaluate effects of mixed-planting

M. citrifolia

with mahogany on establishment of food-supplemented ant colonies (below). Please contact first author for additional information. E-mail: [email protected]. Campus address: 216 Price Hall, Blacksburg VA 24061

the weaver ant,

Conclusions

A complementary series of studies was successfully conducted to conserve and augment weaver ant populations.

• Relocated weaver ant colonies can be conserved by short-term food supplementation • Live mealworms (L) weaver ant formula and are • preferred foods that are cheap and simple to apply • Foods should be given for at least 3 months to ensure colony establishment

M. citrifolia

is a preferred host plant of the ant that is easy to grow and yields medicinal by-products.

profitable

Providing foods directly through supplemental feeding and indirectly by planting alternative host plants with the main crop may well prove to be a reliable approach to growing environmentally-friendly mahogany in partnership with the weaver ant.

Literature Cited

Bluthgen, N. & Fiedler, K. 2004. Preferences for sugars and amino acids and their conditionality in a diverse nectar-feeding ant community.

Animal Ecology

73:155-166.

Journal of

Griffiths, M.W. 2001. The biology and ecology of 74-80 in Floyd, R.B. & Hauxwell, C. (Eds.).

Hypsipyla

shoot borers. Pp.

Proceedings of an International Workshop on Hypsipyla Shoot Borers in Meliaceae

. ACIAR Proceedings Series No 97. Kandy, Sri Lanka, 20-23 August 1996. ACIAR, Canberra.

Lim, G.T. & Kirton, L.G. 2003. A preliminary study on the prospects for biological control of the mahogany shoot borer,

Hypsipyla robusta

(Lep.: Pyral.), by ants (Hymen.: Form.). Pp. 240-244 in

Forestry and Forest Products Research.

FRIM, Malaysia.

Proc. of Intern. Conf. on

Kuala Lumpur, 1-3 October 2001.

Way, M.J. & Khoo, K.C. 1991. Colony dispersion and nesting habits of the ants,

Dolichoderus thoracicus

and

Oecophylla smaragdina

(Hymenoptera: Formicidae), in relation to their success as biological control agents on cocoa.

Bulletin of Entomological Research

81(3):341-350.

Acknowledgements

We thank Ms. Saimas Ariffin, Mr. Saiful Azhari, Mr. Shaiful Amri, Ms.

Nurziah Ishak, Mr. Fadir Ishak (below), Ms. Hidaya, and Mr. Azmi Mahyuddin (Entomology Section, FRIM) for assistance in conducting the experiments, and Dr Ang Lai Hoe (Ecophysiology Section, FRIM) for use of Hobos.

The plant species were identified by Mr Mohd. Asri and Mr Kamarudin Saleh (Botany Section, FRIM). Identification of trophobionts was provided by M. Kosztarab (Virginia Tech) S.H. McKamey and D.R.

Williams (USDA-ARS).

This project was supported by the Fulbright (administered by Department Institute of of Program the State, U.S.

the International Education, and the Malaysian American Commission on Educational Exchange), Virginia Tech and FRIM.